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To meet carbon emissions targets, more than 30 countries have committed to boosting production of renewable resources from biological materials and convert them into products such as food, animal feed and bioenergy. In a post-fossil-fuel world, an increasing proportion of chemicals, plastics, textiles, fuels and electricity will have to come from biomass, which takes up land. To maintain current consumption trends the world will also need to produce 50–70% more food by 2050, increasingly under drought conditions and on poor soils. Depending on bioenergy policies, biomass use is expected to continue to rise to 2030 and imports to Europe are expected to triple by 2020. Europe is forecast to import 80 million tons of solid biomass per year by 2020 (Bosch et al. 2015).

Producing large volumes of seaweeds for human food, animal feed and biofuels could represent a transformational change in the global food security equation andin the way we view and use the oceans. In 2012, global production of seaweeds was approximately 3 million tons dry weight, and growing by 9% per annum. Increasing the growth of seaweed farming up to 14% per year would generate 500 million tons dry weight by 2050, adding about 10% to the world’s present supply of food, generating revenues and improving environmental quality (Table 1). Assuming a conservative average productivity from the best operating modern farms of about 1,000 dry metric tons per km2 (1 kg per m2), this entire harvest could be grown in a sea area of about 500,000 square kilometers, 0.03% of the oceans’ surface area, equivalent to 4.4 percent of the US exclusive economic zone.

With a view to finding out the feasibility of Lakshadweep lagoons for cultivation of Gracilaria edulis in Minicoy experimental culture has been undetaken at four sites. Very encouraging results indicating high potential of about 8.1 fold increase for this species in the lagoon evironments of Minicoy was obtained. Seasonal variations in the growth of the culture seaweed is high-lighted in this account indicating favourable seasons and potential sites.

Fifty five seaweed extracts belonging to 11 species of seaweeds were tested against post operative infectious drug resistant bacteria viz., E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Streptococcus pyogens, Staphylococcus aureus. Among the seaweed extracts, the acetone extracts of Caulerpa cupressoides shows maximum inhibtory activity against E. coli and propanol extracts of Gracilaria edulis shows maximum inhibitory effect against K. pneumoniae. Acetone extracts of Padina tetrastromatica and Laurencia cruciata show maximum inhibitory activity against P. aeruginosa, butanol extracts of Hypnea musciformis, Caulerpa cupressoides and Chaetomorpha linoides show maximum inhibitory effect against S. aureus.

In recent years, microalgal feedstocks have gained immense potential for sustainable biofuel production. Thermochemical, biochemical conversions and transesterification processes are employed for biofuel production. Especially, the transesterification process of lipid molecules to fatty acid alkyl esters (FAAE) is being widely employed for biodiesel production. In the case of the extractive transesterification process, biodiesel is produced from the extracted microalgal oil. Whereas In-situ (reactive) transesterification allows the direct conversion of microalgae to biodiesel avoiding the sequential steps, which subsequently reduces the production cost. Though microalgae have the highest potential to be an alternate renewable feedstock, the minimization of biofuel production cost is still a challenge. The biorefinery approaches that rely on simple cascade processes involving cost-effective technologies are the need of an hour for sustainable bioenergy production using microalgae. At the same time, combining the biorefineries for both (i) high value-low volume (food and health supplements) and (ii) low value- high volume (waste remediation, bioenergy) from microalgae involves regulatory and technical problems. Waste-remediation and algal biorefinery were extensively reviewed in many previous reports. On the other hand, this review focuses on the cascade processes for efficient utilization of microalgae for integrated bioenergy production through the transesterification. Microalgal biomass remnants after the transesterification process, comprising carbohydrates as a major component (process flow A) or the carbohydrate fraction after bio-separation of pretreated microalgae (process flow B) can be utilized for bioethanol production. Therefore, this review concentrates on the cascade flow of integrated bioprocessing methods for biodiesel and bioethanol production through the transesterification and biochemical routes. The review also sheds light on the recent combinatorial approaches of transesterification of microalgae. The applicability of spent microalgal biomass residue for biogas and other applications to bring about zero-waste residue are discussed. Furthermore, techno-economic analysis (TEA), life cycle assessment (LCA) and challenges of microalgal biorefineries are discussed.